High temperature phosphorus containing molding compositions and ceramics



United States Patent U.S. Cl. 260-37 2 Claims ABSTRACT OF THE DISCLOSUREA process for preparing a ceramic molding composition comprising mixinga siliceous compound with a binding composition comprisingphosphonitrilic chloride-polyhydric alcohol condensates.

The present invention relates to the production of ceramics, and morespecifically to a novel ceramic molding composition and temperatureresistance of objects obtained therefrom.

Ceramic materials which are used in modern technology must possess notonly resistance to high temperatures, but must also be dimensionallystable and resistant to impact when in use and during processing.

It is therefore an object of the present invention to provide improvedceramic molding composition.

It is another object to provide a ceramic molding composition from whichaccurately molded high temperature resistant ceramic objects may beprepared.

These and still further objects of the present invention will becomereadily apparent from the following detailed description and specificexamples.

Broadly, the present invention contemplates ceramic molding compositionswhich comprises (1) a particulate, siliceous material, and (2) a bondingcomposition comprising a phosphorus containing compound. Useful hightemperature resistant ceramic objects may be prepared from the abovecompound when the ingredients thereof are (l) blended in the requiredamounts, (2) molded and cured at temperatures sufficient to polymerizethe resin, and finally (3) fired at a temperature in excess of 1000 F.

More specifically, We have found that strong, tough, dimensionallystable, ceramic moldings may be readily obtained by using our novelmolding composition which comprises the following ingredients: (1) fromabout 60 to about 90 parts by weight of a particulate, siliceouscompound such as silica, vermiculite and/or wollastonite, and (2) fromabout to about 40 parts by weight of a binding composition whichcomprises from about 3 to about 6 parts by weight based on phosphorus ofa high temperature bonding agent such as polyphosphonitriles.

To prepare ceramic moldings from our novel compositions, the abovecomponents are preferably intimately admixed in the desired ratio, thenmolded to the desired shape. Since the present composition undergoessubstantially no dimensional changes during curing and firing, theinitial molded shape may be substantially the same size as the desiredfinished article.

Subsequent to molding, the required shape is then preferably cured at atemperature sulficiently high to polymerize the organic resin bondingcomponent. Ordinarily, temperatures on the order of from about 150 C. toabout 250 C. are sufficient for this purpose wherein curing of thethermoset resin is achieved in from about to about 90 minutes.

Subsequent to curing of the molded object, a molded article is obtainedwhich is then ready for firing at temperatures ranging from about 600 toabout 1000 C. The

Patented June 10, 1969 precise time required to fire a given moldedobject depends on the size and shape thereof. However, complete firingis ordinarily obtained at from about 4 to about 10 hours. The firedceramic object contains substantially no carbon and possessessubstantially the same size and shape as the original molded object. Theceramic objects are strong and exceedingly tough and can withstandtemperatures as high as about 1200 C. for indefinite periods. X-rayanalysis of the ceramics indicates the presence of crystalline SiO -P Owhich it is believed acts as the binding agent.

As indicated above, the present method for preparing ceramic objectspreferably comprises three separate steps. They are: (1) the preparationof the molding mixture and the shaping thereof, (2) curing at atemperature sufficient to polymerize the binding component and therebyform a physically durable molded object which readily withstandshandling prior to and during curing, (3) firing at elevatedtemperatures. It is contemplated however, that the immediate curing stepwherein the resin is polymerized may be merged into the final firingstep. However, it is generally preferred that the present moldingoperation be carried out in three individual operations.

The siliceous material utilized in the present molding compositions maybe of a synthetic or naturally occuring origin. Typically, siliceousmaterial such as vermiculite, wollastonite, ground glass, silica fibermay be utilized.

The resin component is one which is compatible with the siliceousmaterial and which preferably cures at a temperature range of from about150' to about 250 C. The thermosetting cyclic phosphonitrilicchloride-polyhydric alcohol condensates may be used. These phosphoruscontaining resins may serve the dual function of thermoset binding agentand phosphorus donating compound.

The phosphorus containing component utilized in the present compositionserves as a high temperature binding agent. That is, when the presentmolded objects are fired at elevated temperatures, substantially allcarbon contributed by the thermoset resin component is driven out of themolded composition. The phosphorus component remains in the compositionto form which appears to be SiO -P O residues. These phosphorus silicaresidues it appears constitute a strong, tough bonding characteristic tothe fired ceramic mass. While the precise nature of the bondingphenomena contributed by phosphorus is not entirely understood, it isbelieved the strength derived from the present composition isattributable to the phosphorus containing component. Typical phosphoruscompounds which may be used are both of semi-organic and totallyinorganic nature. For example, the phosphorus containing compound maycomprise an organic substituted cyclic phosphonitrilic ring system.

While the necessary components of the present molding compositioncomprises a siliceous material, a phosphorus donating compound and aresin, it is contemplated that other reenforcing materials such. asmetallic powders and fragments may be readily incorporated in thepresent ceramic compositions to give a desired characteristic to theresultant article.

The present ceramic compositions find use as high temperature resistantlinings for combustion chambers, insulators and so forth.

Having described the basic aspects of the present invention, thefollowing examples are given to illustrate embodiments thereof.

EXAMPLE I A mixture comprising 65% wollastonite, 31.5% of aphenylphosphonitrilic chloride-hydroquinone condensation productprepared by condensing one mole of (.PNCl) (=phenyl) and three moles ofhydroquinone at C. for 60 min., and 3.5% hexamethylene tetraminewas-molded-at-ZOOO p.s.i-. at a temperature of 450 for one hour. Moldingwas then fired in a muffle furnace at a temperature of 1800 F. for fourhours. A tough, white ceramic object having substantially the samedimensions as the pre-fired molding was obtained. The emission spectrumof the ceramic object indicated phosphorus to be present.

EXAMPLE II EXAMPLE HI A mixture comprising 75 by weight of ground silicafiber, 22.5% by weight of the hydroquinone (PNCI) condensation productdescribed in Example I, and 2.5% by weight of hexamethylene tetraminewas molded in a x 5 x inch mold which was heated at 450 F. for one hour.'Six 5 x /2 x inch samples were then cut from the molding. Three ofthese samples were pyrolized by heating in a mufile furnace at atemperature of 18 F. for 5 hours to produce ceramic strips. Flex-uralstrengths were compared with the unfired samples. The flexural strengthsin terms of psi. at rupture, was 4325 for the unfired material and 2299for the fired material. X-ray analysis indicated the existence of Si-O-P O in the ceramics. Comparison in chemical analysis of the fired andnon-fired products indicated the phosphorus content did not changesignificantly upon firing.

4 EXAMPLE IV To confirm the present belief that the present ceramicmaterials contained an SiO -P O residue which adds to the bindingstrength of the ceramic objects, a mixture comprising 80% colloidal A1 0and 20% by weight of the phenylphosphonitrilic-hydroquinone condensateproduct used in Example III was combined and molded at 2000 psi. at 450F. 'for one hour. This molded object was then fired at 1800 F. for 16hours. A chalky product was obtained which possessed substantially nophysical strength.

It is concluded from this example that the present compositionscontaining both phosphorus and silica yield novel ceramic materialswhich cannot be obtained using other non Si0 containing inorganic fillermaterials commonly used in the preparation of ceramics.

We claim:

1. A ceramic molding composition consisting essentially of (1) 60 to 90parts of a particulate siliceous material and (2) 10 to 40 parts of abinding composition comprising phenylphosphonitrilicchloride-hydroquinone condensation product.

2. A ceramic molding composition consisting essentially of (1) to partsof silica fibers and (2) 10 to 40 parts of a phenylphosphonitrilicchloride-hydroquinone condensation product.

References Cited UNITED STATES PATENTS JAMES E. POER, Primary Examiner.

US. Cl. X.R. 106-39, 46, 63, 69

